The present invention generally relates to methods of making electrical insulators for magnetic cores and more particularly to methods of making slot liners for stator cores of fractional and small integral horsepower motors; to methods of placing such slot liners in core slots; and to methods of making stator assemblies that include such slot liners.
Slotted magnetic cores used in dynamoelectric machines, such as electric motors and generators, have conductors disposed in slots thereof; and it is necessary that a layer of dielectric material separate certain surfaces of the cores and the electrical conductors accommodated thereby. Taking an induction motor stator core, for example, electrical coils are carried in slots that extend axially through the core and that have entrances in communication with a central bore adapted to receive a rotor. These conductors are themselves covered with a layer of insulating material, but additional insulation is usually required along core slots and especially at the ends thereof to reduce (if not prevent) abrasion or other damage of the insulation on the conductors and to prevent grounding of the conductors to the core. Such additional insulation is especially desirable should the coil insulation be abraded, chipped, or cracked, and even more so in the vicinity of the usually sharp edges of the slots at the core end faces. One desirable approach for insulating the slots is the employment of slot liners fabricated from suitable dielectric strip material. Such slot liners are inserted into the core slots either manually or with the use of inserting equipment, as will be understood by persons skilled in the art.
One problem with respect to dynamoelectric machine insulation of the slot liner type is the cost of the insulating material itself, examples of which are polyamide materials, or polyester materials, one specific example of which is polyethylene terephalate and which is available as a film under trade names such as "MYLAR" and "MELINEX". For more economical use of such material, it is generally desirable to use a minimum thickness of such material, so long as adequate insulating and strength properties are not sacrificed. However, it has been found (for strength purposes) that a relatively greater thickness of material is needed for those portions of the slot liners adjacent to the end faces of the core than along the side walls of such slots. Since slot liners usually are made from strip material, this in turn has required the use of thicker material along the slot walls than would otherwise be necessary for obtaining the desired insulating (or dielectric) properties.
In one particular slot liner arrangement that has been offered for sale more than one year prior to the filing of this application, a slot liner is formed by folding opposite ends of a piece of relatively thin insulating material upon itself in a common direction at both ends to form two end portions of double thickness insulating material and then both double thickness end portions are again folded in a common direction to form cuffs at each end portion. The above-mentioned slot liner and other slot liners employing folding of insulating material upon itself in a common direction at both ends thereof reduce the amount of insulating material used for a given insulator.
My work along these lines, however, has revealed that this approach of others of folding thick material upon itself (so that double thicknesses of material will be adjacent the ends or "corners" of slots) should result in manufacturing problems when existing equipment and processes are used to axially insert such slot liners in core slots (as taught for example in Mason U.S. Pat. No. 3,745,394 or Schlaudroff U.S. Pat. No. 3,703,854) or to axially insert windings along such slots (as taught for example in Arnold U.S. Pat. No. 3,579,791; Lauer and Pieper U.S. Pat. No. 3,829,953; or Smith U.S. Pat. No. 3,698,063).
For example, the thin material might be folded on itself to facilitate the axial insertion of slot insulators along core slots, but later axial insertion of windings could tend to unfold the insulator. On the other hand, if the insulator is folded in a direction to facilitate winding insertion, difficulties might be encountered when placing the insulators in the slots.
Accordingly, it would be desirable to provide new and improved methods of making a slot liner which can result in substantial savings in insulating material usage, but which also may facilitate ready insertion of the slot liner in core slots by using proven methods and apparatus, and that would not interfere with using known winding insertion methods.
Accordingly, objects of the present invention are to provide new and improved methods of making slot liners.
Other objects of the present invention are to provide new and improved methods of making insulated dynamoelectric machine stator cores.
Yet other objects of the present invention are to provide new and improved methods of making dynamoelectric machine stator assemblies.